This post will briefly explain the basic components of a geographic information system (GIS) from a technical point of view (for comp sci students).
Part 1
GIS: provides the required tools to perform operations on geospatial data, e.g. QGIS, OpenLayers, Google Maps
Map: representation of geospatial information, shows multiple layers which are stacked over each other in a visual manner
Projection: transformation of the earth shape into a rectangle (2d) or sphere (3d). This process is never lossless, see https://www.thetruesize.com/. Projections can cover only parts of the earth or the whole globe (world projections). World projections are EPSG:3857 and EPSG:4236 (longitude+latitude)
Layer: contains geographical information for a specific topic, e.g. buildings, roads or rails.
Raster Layer: Shows georeferenced pixel-based photos, e.g. satellite photo, air photo or street map (like OpenStreetMap)
Vector Layer: Shows georeferenced, scalable and interactive geometric shapes
Feature: a technical unit represented on a map, e.g. a tree, a rail track, a building, a sea.
Tabular feature data: key value information about the feature, e.g. address of a building
Geometry attribute of a feature: where and in which shape the feature is located on the map
Geometry: a georeferenced shape
Point: single pair of coordinates:
(x,y)LineString: list of coordinates:
[(x1,y1), (x2,y2), (x3,y3)]Polygon: list of coordinates with first and last point connected:
[(x1,y1), (x2,y2), (x3,y3), (x1,y1)]Circle: can either be constructed from a list of coordinates (as polygon, imprecise) or based on a centre and radius
Multi Point, LineString, Polygon: a feature consisting of multiple non-connected geometries might have a composed type.
Style: how to present a feature on the map. Different styles allow a graphical analysis of the features. Therefore, varying styling rules can be built out of the Tabular feature data.
Part 2
Service: Processes the geodata into a consumable format, e.g. render a raster image. Operates as web server.
GeoJSON: JSON based exchange format for Geometries and Tabular feature data
PostGIS: A postgres server instance with the “PostGIS” extension installed
GeoPackage: SQLite based geodata store
WMS: open standard protocol to render raster images out of geospatial data and styling rules
WMTS: same as WMS but pre-rendered into Tiles of a fixed size
WFS: open standard protocol to query Features with Geometries, not Styles!
WFS-T: same as WFS but transactional (allow editing of Features)
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